Priority is claimed with respect to German Application No. 199 27 403.7-16 filed in Germany on Jun. 16, 1999, the disclosure of which is incorporated herein by reference.
The invention relates to a backrest for a vehicle seat.
In the case of so-called rear-end collisions, another vehicle impacts against the rear of one""s own vehicle, or one""s own vehicle reverses into an obstacle. In a first phase, the seat occupant""s head moves rearwards translatively relative to the occupant""s trunk, since the seat occupant""s body or trunk is accelerated forwards by the seat and the head, on account of its inertia, is unable to follow this movement. In a second phase, an accelerated rotation of the head to the rear takes place. The head restraint""s role is essentially to prevent hyperextension of the spinal column in the second phase.
In a known backrest for a vehicle seat of the type mentioned at the beginning (WO 95/11818), the cervical vertebra distortion risk existing in the first phase of the rear-end collision because of the relative translation between the head and upper body is combated by a fixed supporting element in the backrest padding, which supporting element is designed in such a manner that it yields, exclusively in the event of a collision, in such a way that the seat occupant""s back, at least in the shoulder region, dips into the backrest padding and therefore moves rearwards and relative to the head restraint, as a result of which the translation from upper body to the head is avoided. In one exemplary embodiment, the supporting element is designed as a net which is connected to the stiff seat frame by straps which do not permit a substantial rearwards shifting of the net during normal operation. In contrast, in the event of a rear-end collision, the upper part of the net moves rearwards and the seat occupant""s upper body therefore likewise moves rearwards, so that it is brought against the head restraint with substantially reduced relative movement between the head and upper body. The construction used for this is bulky and leads to increased reaction times. In addition, the weight of the backrest, and therefore the weight of the vehicle seat, is not inconsiderably increased.
The invention is based on the object of improving a backrest of the type mentioned at the beginning with regard to minimizing the possibility of cervical vertebra distortions and, in the process, of taking heed that the backrest is of lightweight construction.
The backrest according to the invention has the advantage that by means of the shaped cushion which is integrated in the upper backrest region, there is present, in normal operation, a comfort-orientated seat contour which makes it possible, in the event of a rear-end collision, for the backrest padding to yield inelastically virtually without any delay, thereby ensuring a virtually parallel movement of the upper body and head until the head is intercepted by the head restraint. The gas-filled shaped cushion is extremely light, does not lead to an increase in weight of the backrest and can be used in addition and in a simple manner in order to form the seat contour. If, according to a preferred embodiment of the invention, the rapid elimination of air from the shaped cushion takes place by means of a valve controlled as a function of an acceleration sensor, this valve can also be used in order to fill the shaped cushion, so that the possibility arises of an individually adjustable seat contour.
According to an advantageous embodiment of the invention, the contour, which is present behind the shaped cushion, of the padding front surface facing the seat user is designed in such a manner that when the shaped cushion is deflated, the said contour, together with the head-restraint front surface, forms an optimum supporting surface for the seat user""s head and body. The stiffness of this contour and the stiffness of the head restraint are matched to each other here in such a manner that with further shifting back of the seat occupant in the course of the rear-end collision, a substantially parallel movement of the seat occupant""s head and upper body is ensured. By means of these structural measures, the head and upper body are advantageously aligned with respect to each other, and during the further course of the rear-end collision are kept in this fixed alignment until the crash energy acting upon the seat user is substantially degraded.
The degradation of the crash energy is assisted in that, according to an advantageous embodiment of the invention, an energy-dissipating, irreversibly deformable supporting structure, for example made of open-pore foam, is arranged in the padding behind the shaped cushion.
According to an advantageous embodiment of the invention, in order to suddenly deflate the shaped cushion, a tear-open seam which splits open in the event of a rear-end impact is provided in the shaped cushion. This tear-open seam can be made to split open by body weight, or a sensor sensing the rear-end impact is provided, which sensor pulls open the tear-open seam, for example by means of a ripcord, when an acceleration value is exceeded. A sensor of this type is, for example, an inert mass which, in the event of a rear-end impact, is displaced rearwards relative to the seat and thereby pulls the ripcord.
According to an alternative embodiment of the invention, in order to deflate the shaped cushion, a valve is connected to the shaped cushion, and an acceleration meter and also a control device are provided, the said control device opening the valve when an acceleration value measured by the acceleration meter is exceeded.
In order to accelerate the deflating of the shaped cushion, according to an advantageous development, the valve outlet is connected to a vacuum.
According to an advantageous embodiment of the invention, a second shaped cushion is arranged in the lumbar region of the backrest padding, which shaped cushion is filled with a gaseous medium and is deflated in a defined manner in the event of a rear-end impact. This second shaped cushion in the lumbar region prevents the seat occupant""s body from pressing upwards against the backrest, which is known as ramping. At relatively high crash speeds, the second shaped cushion provides a further deformation path, so that the load on the seat occupant is reduced. In addition, the second shaped cushion can be used to give ideal supporting of the spinal column during normal operation, and the seat contour can be adapted individually to the seat occupant""s back.